A linear polycarbonate resin produced from bisphenol A, etc., is excellent in transparency, heat resistance and mechanical properties, and is widely used in various fields. However, when the above linear polycarbonate resin is used in the fields of extrusion molding, blow molding, injection molding and vacuum molding, a molded product sometimes has a thickness non-uniformity due to a low melt tension, or a drawdown is caused, so that no satisfactory molded articles are obtained in some cases. For overcoming this, there is disclosed a method that uses in polymerization a branched polycarbonate resin obtained by adding a branching agent having three or more functional groups (Patent Documents 1 to 3).
However, in the method of Patent Document 1, the melt tension of a branched polycarbonate resin is increased to some extent. However, when the amount of the branching agent is increased, the polycarbonate resin may be crosslinked and a gel can be generated. The thermal stability which the branched polycarbonate resin requires to have for extrusion molding, blow molding, injection molding and vacuum molding cannot be said to be sufficient.
In the method of Patent Document 2, the branched polycarbonate resin has high melt tension, while it is poor in moldability, and the surface state of a molded article obtained is degraded. Further, the thermal stability that the branched polycarbonate resin requires to have for extrusion molding, blow molding, injection molding and vacuum molding cannot be said to be sufficient.
In the method of Patent Document 3, the branched polycarbonate resin has a relatively high melt tension. However, when the amount of a branching agent is increased, the polycarbonate resin is crosslinked to possibly generate a gel, therefore no satisfactory branching property is obtained. Further, a gel might get mixed with a molded article, and it impairs the impact resistance and transparency of the polymer.    (Patent Document 1) JP-A 59-047228    (Patent Document 2) Japanese Patent No. 3,693,462    (Patent Document 3) JP-A 2005-126477